Unraveling a novel precipitate enrichment dependent strengthening behaviour in nickel-based superalloy

Abstract

In the past 100 years, precipitation strengthening has always been extremely important pathway to resist the deformation of material due to significantly improving matrix strength. The size deviation degree and the space distribution of precipitates have a great influence on the strength reported by recent experiments, however, this internal mechanism has been largely ignored and incompletely understood until to now in nickel-based superalloy. Herein, our work systematically clarifies the effect of size deviation degree on the complex interaction between precipitates and dislocations in a 3D space, to explore the enrichment of precipitation size and spatial distribution mediated strengthening mechanism. Especially, a new statistical approach using minimal spanning tree to describe the variation of the inter-precipitate spacing is proposed for accurately assessing contribution of the spatially randomly distributed precipitates to the strength. Importantly, the maximal precipitation strengthening occurs when the size variance is equal to the average size, due to high frequent interactions of dislocations with precipitations to cause the strong pinning and the distorted dislocation-line structure. The slight precipitate spatial enrichment corresponding to the optimal strength makes the precipitates tend to be evenly distributed on the slip plane, which results in more precipitates on the moving dislocation line, and then leads to a severely curved dislocation, arising the high dislocation line tension to inhibit its movement. A robustness test performed on nickel-based superalloys suggests our proposed method would be robust to accurately evaluate performance without experiment, and simultaneously gives optimal precipitate distributions. The current work provides a new strategy to adjust the distribution mode of precipitates to enhance mechanical properties of precipitate hardened alloys.